Unwelcome guests in the garden

Wildlife is good and necessary for a healthy ecosystem, we know that, but there are some species that are less welcome than others. Top of my list of Unwelcome Visitors this week is the horsefly (Haematopota pluvialis, which means ‘blood-drinker of the rains’), also known as the cleg or clegg fly.

Picture from Wikimedia Commons

These large flies are a common sight to anyone who spends a lot of time outdoors and whilst their name suggests that they bother horses, they also bother humans. It is the female who bites as she needs a blood meal in order to make eggs. Horseflies can easily bite through the skin of horses and cows, so the fragile skin of a human is a small barrier to them. Even putting on gloves and a long-sleeved shirt is nothing to them, as their serrated, scimitar-like mandibles easily cut through them. Once they find your skin, they use these mandibles to slice into the flesh and drink blood, some will even take a piece of you away to consume later.

Horseflies are quite big, up to 12 millimetres (0.47 in) long, and the
female is recognisable by her large, brightly irridescent eyes.

Picture from Wikimedia Commons

The most vexing thing about female horseflies is that they fly silently and you often don’t realise you’ve been bitten until you notice the blood around the bite and then it’s too late. Sometimes the horsefly has chewed into another mammal earlier on and so leaves behind bacteria in the wound, which then becomes infected.

The damp, warm conditions we’ve had lately are perfect for horseflies and females will be out and about busily looking for a meal of blood so they can create the next generation. So how to avoid being bitten? Slathering on the insect repellent helps, though doesn’t stop them entirely, but recent research using horses has shown that it isn’t only our smell that attracts these wretched creatures, but the type of light reflected from fabrics, hair and fur. Research has shown that “the insects were most attracted to dark-colored horses, compared with white horses, because darker coats reflected light waves oriented in the same direction. This polarized light was the same as that reflected from pools of water, where the flies lay their eggs. White coats didn't reflect this type of polarized light.”

Stripes, it seems, also confuse horseflies because they reflect multiple light patterns. So maybe I should wear Zebra-striped clothes when I’m gardening. I’d certainly show up to humans, if not the flies.